Ebean findPagedList() throw Exception的分析处理过程

谁借莪１个温暖的怀抱￠ 2022-06-06 11:07 174阅读 0赞

# Ebean findPagedList() throw Exception的分析处理过程 #

--------------------

## 一、定义User    ##

>     import javax.persistence.Column;
>     import javax.persistence.Entity;
>     import javax.persistence.Id;
>     import javax.persistence.Table;
>     
>     @Entity
>     @Table(name = "t_user")
>     public class User {
>         @Id
>         private String id;
>         @Column
>         private String username;
>     
>         public String getId() {
>             return id;
>         }
>     
>         public void setId(String id) {
>             this.id = id;
>         }
>     
>         public String getUsername() {
>             return username;
>         }
>     
>         public void setUsername(String username) {
>             this.username = username;
>         }
>     }

## 二、执行测试 ##

>     @Test
>         public void testFindPageList() {
>             Query<User> find = Ebean.find(User.class);
>             find.setMaxRows(1);
>             find.setFirstRow(1);
>             System.out.println(find.findPagedList().getList());
>         }
> 
> 抛出Exception：Caused by: java.lang.IllegalStateException: Bean class User is not enhanced?
> 
> ![Center][]  
>

## 三、分析过程 ##

> **step1**
> 
> 进入BeanDescriptorManager.java:1442查看错误处，看到抛出Exception这里有个hasEntityBeanInterface的校验：  
> 
> 
> ![Center 1][]  
> 
> 
> 进入到hasEntityBeanInterface方法，源码如下：  
> 
> 
>     private boolean hasEntityBeanInterface(Class<?> beanClass) {
>         Class<?>[] interfaces = beanClass.getInterfaces();
>         Class[] var3 = interfaces;
>         int var4 = interfaces.length;
>     
>         for(int var5 = 0; var5 < var4; ++var5) {
>             Class<?> anInterface = var3[var5];
>             if (anInterface.equals(EntityBean.class)) {
>                 return true;
>             }
>         }
>     
>         return false;
>     }
> 
> **由此可知，Entity Bean必须实现一个EntityBean的接口（在网上看到的都没有实现这个接口和集成Model的，不知道是版本问题还是用的方式不对）**  
>   
> 
> 
> **step2**
> 
> User实现EntityBean接口：  
> 
> 
>     import io.ebean.bean.EntityBean;
>     import io.ebean.bean.EntityBeanIntercept;
>     
>     import javax.persistence.Column;
>     import javax.persistence.Entity;
>     import javax.persistence.Id;
>     import javax.persistence.Table;
>     import java.beans.PropertyChangeListener;
>     
>     @Entity
>     @Table(name = "t_user")
>     public class User implements EntityBean {
>         @Id
>         private String id;
>         @Column
>         private String username;
>     
>         public String getId() {
>             return id;
>         }
>     
>         public void setId(String id) {
>             this.id = id;
>         }
>     
>         public String getUsername() {
>             return username;
>         }
>     
>         public void setUsername(String username) {
>             this.username = username;
>         }
>     
>         public String[] _ebean_getPropertyNames() {
>             return new String[0];
>         }
>     
>         public String _ebean_getPropertyName(int i) {
>             return null;
>         }
>     
>         public String _ebean_getMarker() {
>             return null;
>         }
>     
>         public Object _ebean_newInstance() {
>             return null;
>         }
>     
>         public void addPropertyChangeListener(PropertyChangeListener propertyChangeListener) {
>     
>         }
>     
>         public void removePropertyChangeListener(PropertyChangeListener propertyChangeListener) {
>     
>         }
>     
>         public void _ebean_setEmbeddedLoaded() {
>     
>         }
>     
>         public boolean _ebean_isEmbeddedNewOrDirty() {
>             return false;
>         }
>     
>         public EntityBeanIntercept _ebean_getIntercept() {
>             return null;
>         }
>     
>         public EntityBeanIntercept _ebean_intercept() {
>             return null;
>         }
>     
>         public void _ebean_setField(int i, Object o) {
>     
>         }
>     
>         public void _ebean_setFieldIntercept(int i, Object o) {
>     
>         }
>     
>         public Object _ebean_getField(int i) {
>             return null;
>         }
>     
>         public Object _ebean_getFieldIntercept(int i) {
>             return null;
>         }
>     }
> 
> 执行测试，抛出Exception：
> 
> ![Center 2][]  
> 
> 
> 进入BeanPropertiesReader.java:43查看错误处，看到getProperties源码如下：  
> 
> 
>     private String[] getProperties(Class<?> clazz) {
>         try {
>             Field field = clazz.getField("_ebean_props");
>             return (String[])((String[])field.get((Object)null));
>         } catch (Exception var3) {
>             throw new IllegalStateException("Error getting _ebean_props field on type " + clazz, var3);
>         }
>     }
> 
> 这里获取一个 public static的 \_ebean\_props字段，因为这个字段存储的是当前实体类（ User）对应数据库的字段，所以用 field.get((Object)null)来限制该字段必须是 public static字段。
> 
>   
> 
> 
> **step3**
> 
> 增加\_ebean\_props字段后，再次执行测试，抛出Exception：
> 
> ![Center 3][]
> 
> 进入到BeanDescriptor.java:523查看错误处，看到如下代码（这里的\_ebean\_getIntercept()就是User实现的EntityBean的\_ebean\_getIntercept()）：
> 
>     EntityBeanIntercept ebi = this.prototypeEntityBean._ebean_getIntercept();
>                 this.idPropertyIndex = this.idProperty == null ? -1 : ebi.findProperty(this.idProperty.getName());
> 
>   
> 
> 
> **step4**
> 
> 重写 User中的 \_ebean\_getIntercept()：
> 
>     public EntityBeanIntercept _ebean_getIntercept() {
>             return new EntityBeanIntercept(this);
>         }
> 
> 执行测试，发现结果字段值均为null：
> 
> ![Center 4][]  
>   
> **step5**
> 
> Debugger跟踪源码运行，发现设置属性值的方法在EnhanceBeanPropertyAccess.Setter.set(...)方法中会调用实体类的\_ebean\_setField(...)方法对属性进行赋值操作（**即赋值操作由EntityBean.\_ebean\_setField(...)方法完成**）。  
> 
> 
> 重写User的\_ebean\_setField方法：  
> 
> 
>     public void _ebean_setField(int i, Object o) {
>         try {
>             Field field = this.getClass().getDeclaredField(get_ebean_props()[i]);
>             field.setAccessible(true);
>             field.set(this, o);
>         } catch (Exception e) {
>             e.printStackTrace();
>         }
>     }
> 
> 执行测试，运行结果如下：
> 
> ![Center 5][]  
>

## 四、整理后的代码 ##

> 定义AbstractEntityBean，实现EntityBean接口：
> 
>     import io.ebean.bean.EntityBean;
>     import io.ebean.bean.EntityBeanIntercept;
>     
>     import java.beans.PropertyChangeListener;
>     import java.lang.reflect.Field;
>     
>     public abstract class AbstractEntityBean implements EntityBean {
>         // 因为每个实体类都需要一个静态的_ebean_props属性，所以这里定义一个方法获取这个静态属性方便下面的代码调用
>         public abstract String[] get_ebean_props();
>     
>         public String[] _ebean_getPropertyNames() {
>             return get_ebean_props();
>         }
>     
>         public String _ebean_getPropertyName(int i) {
>             return null;
>         }
>     
>         public String _ebean_getMarker() {
>             return null;
>         }
>     
>         public abstract Object _ebean_newInstance();
>     
>         public void addPropertyChangeListener(PropertyChangeListener propertyChangeListener) {
>     
>         }
>     
>         public void removePropertyChangeListener(PropertyChangeListener propertyChangeListener) {
>     
>         }
>     
>         public void _ebean_setEmbeddedLoaded() {
>     
>         }
>     
>         public boolean _ebean_isEmbeddedNewOrDirty() {
>             return false;
>         }
>     
>         public EntityBeanIntercept _ebean_getIntercept() {
>             return new EntityBeanIntercept(this);
>         }
>     
>         public EntityBeanIntercept _ebean_intercept() {
>             return null;
>         }
>     
>         public void _ebean_setField(int i, Object o) {
>             try {
>                 Field field = this.getClass().getDeclaredField(get_ebean_props()[i]);
>                 field.setAccessible(true);
>                 field.set(this, o);
>             } catch (Exception e) {
>                 e.printStackTrace();
>             }
>         }
>     
>         public void _ebean_setFieldIntercept(int i, Object o) {
>         }
>     
>         public Object _ebean_getField(int i) {
>             return null;
>         }
>     
>         public Object _ebean_getFieldIntercept(int i) {
>             return null;
>         }
>     }
> 
> 修改User，继承AbstractEntityBean，实现EntityBean接口（因为Class.getInterfaces()只能获取到当前类实现的接口，所以这里再实现一次）：  
> 
> 
>     import io.ebean.bean.EntityBean;
>     
>     import javax.persistence.Column;
>     import javax.persistence.Entity;
>     import javax.persistence.Id;
>     import javax.persistence.Table;
>     
>     @Entity
>     @Table(name = "t_user")
>     public class User extends AbstractEntityBean implements EntityBean {
>         public static String[] _ebean_props = new String[] {"id", "username"};
>         @Id
>         @Column(name = "id")
>         private String id;
>         @Column
>         private String username;
>     
>         public String getId() {
>             return id;
>         }
>     
>         public void setId(String id) {
>             this.id = id;
>         }
>     
>         public String getUsername() {
>             return username;
>         }
>     
>         public void setUsername(String username) {
>             this.username = username;
>         }
>     
>         @Override
>         public String[] get_ebean_props() {
>             return _ebean_props;
>         }
>     
>         @Override
>         public Object _ebean_newInstance() {
>             return new User();
>         }
>     
>         @Override
>         public String toString() {
>             return "User{" +
>                     "id='" + id + '\'' +
>                     ", username='" + username + '\'' +
>                     '}';
>         }
>     }
> 
> 测试代码TestDBConnection
> 
>     import io.ebean.Ebean;
>     import io.ebean.Query;
>     import org.junit.Test;
>     
>     public class TestDBConnection {
>         @Test
>         public void test() {
>             System.out.println("cnt : " + Ebean
>                     .createSqlQuery("select count(0) as cnt from t_user").findOne()
>                     .getInteger("cnt"));
>         }
>     
>         @Test
>         public void testFindPageList() {
>             Query<User> find = Ebean.find(User.class);
>             find.setMaxRows(1);
>             find.setFirstRow(1);
>             System.out.println(find.findPagedList().getList());
>         }
>     }

## 五、总结    ##

> 这种不与其他框架集成的方式：
> 
>  *  实体类需要实现EntityBean接口
>  *  实体类需要有一个public static的\_ebean\_props字段存储查询的字段名  
>     
>  *  实体类中的\_ebean\_getIntercept()返回值不能为null（即不能是空实现）  
>     
>  *  查询数据后Ebean会调用\_ebean\_setField方法为属性赋值，实体类中的\_ebean\_setField方法不能是空实现

[Center]: /images/20220606/a1749a2890bc4c3984698ce3cb361702.png
[Center 1]: /images/20220606/cc3e61cbfec14c028b1b755199810a80.png
[Center 2]: /images/20220606/073b0bf148dc410cb8230f11f3e00970.png
[Center 3]: /images/20220606/d1df201c58de43b2a7e4a35c47df05db.png
[Center 4]: /images/20220606/ee5d6b15ac714d7983984346a2888443.png
[Center 5]: /images/20220606/1c64b2de1f044ee0a302c2ada894cb43.png